Leptospirosis outbreak after severe flash flooding in Krabi, Thailand, January–February 2017

Abstract

Background: Upper Southern Thailand experienced widespread flash floods in January 4th, 2017. One week later, a number of suspected leptospirosis increased sharply in Krabi province with 2 fatal cases were reported. We started outbreak investigations with aims to confirm diagnosis with outbreak, describe etiology and behavioral risk and recommend control and prevention measures.
Methods: Descriptive study was conducted. In active case finding, a suspected case was defined as a person who lives in Krabi province and had fever plus two of the following symptoms; severe headache, myalgia, calf pain, red eyes and jaundice during January 1st–February 8th, 2017. Probable case was a suspected case with severe illness but lab was not confirmed. A lab-confirmed case was positive either PCR or IFA or MAT or ELISA. Environmental and domestic animals reservoirs study was done for Leptospira PCR and culture including MAT for leptospira serology.
Results: A total of 62 cases (61 from Meuang district) met the case definition and confirmed outbreak. Of those, 23 were lab-confirmed and 2 and 37 were probable and suspected cases. Male to female ratio was 1.3 : 1. Median age was 39.5 years (2-80 years) among 23 confirmed and 2 probable cases, 2 died (CFR 3.20 %). The confirmed cases were tested positive by IFA 45.1 %, MAT 29.47%, ELISA 26.3% and PCR 3.20 %. The first and last onset was on January 5th and February 2nd, 2017 and peak at third week after flooding. Common clinical presentation was fever (100%), severe myalgia (92%) headache (88%). calf pain (60%) chill (60%) dark urine (60%) and jaundice (32%) and behaviors risk was common among confirmed/probable cases demonstrated having wound at foot (79%) and open wound exposure with water and mud (91%) were significant different among suspected cases. The most common serogroup in human case were Shermani (87%) and Sejroe (47%). Leptospira spp. was also detected by culture in 6 soil samples (100%) but 9 natural water samples were negative. The animal serology for MAT was positive in 3 dogs (100%) and 7 bovine (100%). But 13 rodents, 2 cats and 7 swine were all negative. The most common serogroups in animal were Ranarum (80%), Sejroe (70%) Hebdomadis (40%) and Mini ND (40%). There were lab-confirmed leptospirosis among 2 dogs and one of them died.
Conclusions: A lab-confirmed leptospirosis outbreak occurred in Krabi province following the severe flash floods. IFA is the best test for leptospirosis confirmation. After aggressive surveillance and control implementation for leptospirosis outbreak in the province for a month, the outbreak was terminated on February 8th 2017, when cases had decrease to baseline level (< 1 case/day) and no fatal case reported. Therefore, interventions should be implemented in the affected farm to prevent and control the spread of Leptospira to animals, humans and environment. Protective body wearing after flooding was crucial prevention. Early detection and treatment is a mortality reduction.